The present invention relates to semiconductor electronic devices, and, more particularly, to devices with ballistic carrier transport.
Ballistic transport of electrons in short-channel field effect transistors and through the base of a heterojunction bipolar transistor is a much-discussed phenomenom that becomes increasingly important as the dimensions of transistors are shrunk well below the one micron scale. Such ballistic transport offers the possibility of higher switching speeds due to the minimal time that the carriers are in the channel or base. See, for example, M. Shur and L. Eastman, Ballistic Transport in Semiconductor at Low Temperatures for Low-power High-Speed Logic, 26 IEEE Tr.Elec.Dev. 1677 (1979). Ballistic transport affecting performance can also occur in devices such as IMPATT diodes that have a well-defined drift region.
However, the ballistic effect appears to depend upon the initial (injection) velocity of the carriers, so that the distance traveled prior to scattering is a function of injection energy. See, J. Tang and K. Hess, Investigation of Transient Electronic Transport in GaAs Following High Energy Injection, 29 IEEE Trans. Elec. Dev. 1906 (1982). But known devices inject carriers with a large spread of energies and fail to fully exploit ballistic transport due to the significant portion of carriers with suboptimal injection energies.
Thus it is a problem to provide devices in which the carriers are injected with energies in a narrow band in order to provide full ballistic transport.